The Historical Development of Quantum Theory. Volume 6: The Completion of Quantum Mechanics, 1926-1941 The Historical Development of Quantum Theory. Volume 6: The Completion of Quantum Mechanics, 1926-1941 Jagdish Mehra and Helmut Rechenberg Part 1: The Probability Interpretation and the Statistical Transformation Theory, the Physical Interpretation, and the Empirical and Mathematical Foundations of Quantum Mechanics 1926-1932. Springer-Verlag, New York. 2000. $129.00, $69.95 paper (670 pp.). ISBN 0-387-98971-4, ISBN 0-387-95181-4 paper Part 2: The Conceptual Completion and the Extensions of Quantum Mechanics 1932-1941. Epilogue: Aspects of the Further Development of Quantum Theory 1942-1999. Springer-Verlag, New York. 2001. $149.00, $69.95 paper (941 pp.). ISBN 0-387-95086-9, ISBN 0-387-95182-2 paper